U.S. patent application number 12/676633 was filed with the patent office on 2011-06-23 for motor-driven power steering control appartus.
This patent application is currently assigned to MITSUBISHI ELECTRIC CORPORATION. Invention is credited to Masaya Endo, Isao Kezobo, Takayuki Kifuku, Masahiko Kurishige, Masaki Matsushita, Seiji Sawada.
Application Number | 20110153162 12/676633 |
Document ID | / |
Family ID | 40795200 |
Filed Date | 2011-06-23 |
United States Patent
Application |
20110153162 |
Kind Code |
A1 |
Kezobo; Isao ; et
al. |
June 23, 2011 |
MOTOR-DRIVEN POWER STEERING CONTROL APPARTUS
Abstract
A motor-driven power steering control apparatus is achieved,
which uses a small-amplitude pass filter, the filter filtering out
a component having a small amplitude, to remove a steering
component from dynamic state quantity such as a rotational speed
signal, and to accurately extract only a vibration component having
a small amplitude compared with the steering component, and
controls the vibration component to be reduced.
Inventors: |
Kezobo; Isao; (Tokyo,
JP) ; Kurishige; Masahiko; (Tokyo, JP) ; Endo;
Masaya; (Tokyo, JP) ; Kifuku; Takayuki;
(Tokyo, JP) ; Sawada; Seiji; (Tokyo, JP) ;
Matsushita; Masaki; (Tokyo, JP) |
Assignee: |
MITSUBISHI ELECTRIC
CORPORATION
Tokyo
JP
|
Family ID: |
40795200 |
Appl. No.: |
12/676633 |
Filed: |
December 14, 2007 |
PCT Filed: |
December 14, 2007 |
PCT NO: |
PCT/JP07/74113 |
371 Date: |
March 5, 2010 |
Current U.S.
Class: |
701/42 |
Current CPC
Class: |
B62D 5/0472 20130101;
B62D 5/0463 20130101 |
Class at
Publication: |
701/42 |
International
Class: |
B62D 6/00 20060101
B62D006/00 |
Claims
1. A motor-driven power steering control apparatus, including a
torque sensor detecting steering torque applied by a driver, a
torque controller calculating an assist torque current assisting
the steering torque based on a steering torque signal detected by
the torque sensor, and a motor generating assist torque with the
assist torque current, comprising: dynamic state quantity detection
means detecting dynamic state quantity of the motor-driven power
steering control apparatus or a car; a small-amplitude pass filter
filtering out a vibration component having a small amplitude
compared with a steering component from detection output of the
dynamic state quantity detection means; and vibration suppression
control means reducing a vibration component signal obtained by the
small-amplitude pass filter; wherein a feedback control loop,
including addition/subtraction between the assist torque current
being output of the torque controller and a vibration suppression
current being output of the vibration suppression control means, is
established, thereby a vibration component of the motor is
suppressed.
2. The motor-driven power steering control apparatus according to
claim 1, wherein, the small-amplitude pass filter is configured of
a hysteresis filter being inputted with an output signal of the
dynamic state quantity detection means, and performing hysteresis
function processing having a hysteresis range corresponding to the
vibration component, and a subtractor subtracting an output signal
of the hysteresis filter from the output signal of the dynamic
state quantity detection means.
3. The motor-driven power steering control apparatus according to
claim 1, wherein, the dynamic state quantity detection means
includes rotational speed detection means detecting rotational
speed of the motor.
4. The motor-driven power steering control apparatus according to
claim 1, wherein, the dynamic state quantity detection means
includes a torque sensor detecting the steering torque signal.
5. The motor-driven power steering control apparatus according to
claim 1, wherein, the dynamic state quantity detection means
includes rotation angle detection means detecting a rotation angle
of the motor, and rotational speed calculation means calculating
rotational speed from a detected rotation angle signal.
Description
TECHNICAL FIELD
[0001] The present invention relates to a motor-driven power
steering control apparatus assisting steering force of a car
driver, and particularly relates to a motor-driven power steering
control apparatus that may suppress vibration due to torque ripple
or disturbance.
BACKGROUND ART
[0002] In a motor-driven power steering control apparatus that
provides assist power generated by an electric motor in accordance
with steering torque applied to a handle by a car driver, assist
torque approximately proportional to steering torque is determined,
and a torque proportional gain, which keeps such a proportional
relationship, is set large so that steering force of a driver is
reduced and smoothed, and besides, vibration such as torque ripple
produced by a motor or disturbance transmitted from a road surface
is suppressed, improving feeling of the driver.
[0003] In the motor-driven power steering control apparatus of this
type proposed in the past, a mixed filter including a low-pass
filter (LPF) and a high-pass filter (HPF) is used to suppress the
vibration such as motor torque ripple or road surface disturbance,
a steering component is extracted by the LPF to control steering
assist torque, and a high-frequency vibration component such as
torque ripple is extracted by the HPF, and the high-frequency
vibration component is controlled by a different controller
(different gain) from a controller for the low-frequency vibration
component (for example, refer to patent document 1).
[0004] Moreover, a motor-driven power steering control apparatus is
previously proposed, in which a bandpass filter (BPF) is used to
extract a vibration component of motor rotation speed or angular
velocity of a steering angle, and a signal as a product of the
vibration component multiplied by a gain is subtracted from a
target current so that a new target current is set, thereby
negative feedback control of angular velocity is established to
reduce vibration (for example, refer to patent document 2).
[0005] Besides, there exist a motor-driven power steering control
apparatus having hysteresis processing means that filters a
steering torque signal by using a hysteresis function in order to
remove small variation such as bit variation from the steering
torque signal (for example, refer to patent document 3). [0006]
Patent document 1: Japanese Patent No. 2838053 [0007] Patent
document 2: JP-A-2003-26022 [0008] Patent document 3:
JP-A-2004-170174
DISCLOSURE OF THE INVENTION
[0009] Problems that the Invention is to Solve
[0010] In the previous motor-driven power steering control
apparatus as in the patent document 1 or 2, the high-pass filter
(HPF) and low-pass filter (LPF) or the bandpass filter (BPF) are/is
used in extracting a vibration component such as torque ripple or
road surface disturbance. For example, when a frequency band of
torque ripple produced by a motor is separate from a frequency band
of disturbance transmitted from a road surface, only one frequency
band component may be extracted. In addition, when the vibration
component such as torque ripple or road surface disturbance is even
partially overlapped with a frequency band of a steering component,
accurate extraction may not be performed, and consequently not all
vibration components over a wide band have been able to be
suppressed.
[0011] The method performed in the previous motor-driven power
steering control apparatus as that of the patent document 3, in
which a signal is filtered by using the hysteresis function to
remove small vibration such as bit variation, has had a problem
that the vibration component may not be extracted.
[0012] The invention was made to solve the above problems, and an
object of the invention is to achieve a motor-driven power steering
control apparatus that may accurately extract a vibration component
such as torque ripple produced by a motor or disturbance
transmitted from a road surface, and may control such a vibration
component to be easily reduced.
Means for Solving the Problems
[0013] A motor-driven power steering control apparatus, including a
torque sensor detecting steering torque applied by a driver, a
torque controller calculating an assist torque current assisting
the steering torque based on a steering torque signal detected by
the torque sensor, and a motor generating assist torque with the
assist torque current, is characterized by having dynamic state
quantity detection means detecting dynamic state quantity of the
motor-driven power steering control apparatus or a car; a
small-amplitude pass filter filtering out a vibration component
from detection output of the dynamic state quantity detection
means; and vibration suppression control means reducing a vibration
component signal obtained by the small-amplitude pass filter;
wherein a feedback control loop, including addition/subtraction
between the assist torque current being output of the torque
controller and a vibration suppression current being output of the
vibration suppression control means, is established, thereby a
vibration component of the motor is suppressed.
ADVANTAGE OF THE INVENTION
[0014] The motor-driven power steering control apparatus of the
invention is characterized by using the small-amplitude pass
filter, thereby a motor-driven power steering control apparatus may
be advantageously achieved, which may accurately extract a
vibration component having a small amplitude compared with a
steering component, such as torque ripple produced by a motor or
disturbance from a road surface, and may efficiently reduce such a
vibration component by using a feedback control loop.
BEST MODE FOR CARRYING OUT THE INVENTION
Embodiment 1
[0015] FIG. 1 is a block diagram showing a configuration of a
motor-driven power steering control apparatus of embodiment 1 of
the invention. While detailed description of the motor-driven power
steering apparatus itself is omitted herein, a previously known
configuration may be used, and a configuration described in each of
the patent documents 1 and 2 may be referred, for example.
[0016] In the figure, steering torque TO in driver steering is
detected by a torque sensor 1 using a known torsion bar or the
like, and a torque controller 2 calculates an assist torque current
Ia to be provided to a motor 5 based on such torque sensor output .
On the other hand, rotational speed of the motor 5 is detected by a
known rotational speed detection means 7.
[0017] Next, a rotational speed signal Sn outputted by the
rotational speed detection means 7 is filtered by a small-amplitude
pass filter 8 having an input/output characteristic as shown in
FIG. 2, thereby a steering component is removed from the rotational
speed signal Sn and only a vibration component signal Sb is
extracted. The small-amplitude pass filter 8 extracts only a
vibration component having a small amplitude compared with the
steering component, and how to configure the filter is described in
detail later.
[0018] A vibration suppression current Is is calculated by a
vibration suppression control means 9 based on the vibration
component signal Sb extracted by the small-amplitude pass filter 8,
and the current Is is subtracted from the assist torque current Ia
from the torque controller 2 by a subtractor 10, thereby a target
current It to control the motor 5 is obtained. Current control
means 3 controls the calculated target current It and a current Id
detected by current detection means 6 to corresponds to each other,
and outputs a voltage instruction signal Sv such as PWM signal to a
drive circuit 4 including an H bridge circuit or the like, so that
the drive circuit 4 outputs a drive current corresponding to the
PWM signal to the motor 5. The motor 5 generates assist torque
assisting steering force of a steering shaft applied by a
driver.
[0019] Not all configuration blocks of the control apparatus shown
in FIG. 1 are configured by hardware, and a configuration from each
of the output torque signal TO of the torque sensor 1 and the
signal Sn detected by the rotational speed detection means 7 to
calculation of the target current It by the subtractor 10, or to
the voltage instruction signal Sv outputted by the current control
means 3 is configured by software using a microcomputer. The
microcomputer includes a central processing unit (CPU), a read-only
memory (ROM), a random access memory (RAM), an interface (IF) and
the like as well known, and sequentially extracts programs stored
in the ROM to perform desired calculation in the CPU, and
temporarily stores a calculation result into the RAM, thereby the
software is executed and thus predetermined control operation is
performed.
[0020] Operation of the motor-driven power steering control
apparatus configured as above is described according to a flowchart
of FIG. 3. First, a steering torque signal .tau.0 being output of
the torque sensor 1 is read by the microcomputer, and stored into a
memory in step S101. Then, a rotational speed signal Sn read from
the rotational speed detection means 7 is stored into the memory in
step S102. Next, the assist torque current Ia is calculated by the
torque controller 2 based on the steering torque signal .tau.0, and
output thereof is stored into the memory in step S103. Here, the
torque controller 2 may be designed in a known manner, for example,
in a manner that the current is calculated based on predetermined
map data.
[0021] Next, the vibration component signal Sb is calculated by the
small-amplitude pass filter 8 based on the rotational speed signal
Sn read from the rotational speed detection means 7, and stored
into the memory in step S104. Next, the vibration suppression
current Is is calculated by the vibration suppression control means
9 based on the vibration component signal Sb being output of the
small-amplitude pass filter 8, and stored into the memory in step
S105. Then, the subtractor 10 subtracts the vibration suppression
current Is from the assist torque current Ia outputted by the
torque controller 2 so that the target current It is determined in
step S106. Operation from the step S101 to the step S106 is
repeated for each control sample to calculate each target current
It.
[0022] Next, the small-amplitude pass filter 8 is described. As
shown in FIG. 2, the small-amplitude pass filter has a property
that while a variation component having a level equal to or larger
than a level B is saturated and not outputted, a variation
component having a level equal to or smaller than the level B,
which appears near a particular operating point of an input signal,
is directly outputted as variation having a level equal to or
smaller than the level B. Size of such a variation range, namely,
size of a hysteresis range H can be correspondingly set with size
of a vibration component to be desirably extracted as a reference.
For example, a variation component included in the rotational speed
signal is about 0.025 to 0.25 rad/s in terms of angular velocity
about a handle axis, and a variation component included in the
steering torque signal is also about 0.025 to 0.25 Nm. Such
amplitude values are expressed as half amplitude values
respectively.
[0023] FIG. 4 is a block diagram showing a typical configuration
example of the small-amplitude pass filter 8, the filter 8 being
configured of a hysteresis filter 21 that is inputted with an
output signal of the rotational speed detection means 7, and
performs hysteresis processing having a hysteresis range
corresponding to the vibration component, and a subtractor 22 that
subtracts an output signal of the hysteresis filter 21 from the
output signal of the rotational speed detection means 7. The input
signal Sn outputted by the rotational speed detection means 7 is
branched, and the branched signal is filtered through a hysteresis
filter 21 into a signal H0, and the signal HO is subtracted from
the input signal Sn so that the vibration component signal Sb is
obtained. If the small-amplitude pass filter 8 is designed in a
manner of FIG. 4, the filter 8 may be easily configured using
typical elements.
[0024] FIG. 5 shows temporal waveforms of signals of respective
portions of the small-amplitude pass filter 8 shown in FIG. 4,
wherein (a) is a waveform diagram of the input signal Sn, (b) is a
waveform diagram of the output signal HO of the hysteresis filter
21, and (c) is a waveform diagram of the output signal Sb. In each
figure, a vibration component included in the rotational speed
signal is expressed as a value (rad/s) in terms of angular velocity
about a handle axis. The input signal Sn shown in (a) has a
vibration component, and furthermore, has a steering component Ps
shown by a dashed-dotted line as a large amplitude component. The
hysteresis output HO shown in (b) has a waveform attenuated in
vibration component compared with the input signal Sn. The output
signal Sb shown in (c) is a calculation result of a subtractor 22
on the hysteresis output HO and the input signal Sn, where the
steering component Ps is removed from the input signal Sn, and only
the vibration component Sb is extracted from the signal Sn.
[0025] In this case, amplitude of the vibration component Sb
corresponds to a hysteresis range H (0.03 to 0.04 in half
amplitude), and is attenuated by S compared with amplitude of the
input signal Sn (0.05 in half amplitude), showing a fact that
hysteresis processing is performed. It will be appreciated that the
hysteresis range H is appropriately adjusted, thereby the amount of
the attenuation may be controlled. Generally, the vibration
component is characteristically small compared with the steering
component Ps being a main component. Therefore, the small-amplitude
pass filter 8 extracting only a component having a small amplitude
compared with the steering component Ps may remove the steering
component Ps, and may accurately extract the vibration component
Sb.
[0026] Next, the vibration suppression control means 9 is
described. For example, the vibration suppression control means 9
includes means as shown in FIGS. 6(a) to 6(d) as typical examples.
Each example is a known configuration example, and any other
control means may be used. Hereinafter, the typical examples of
FIG. 6 are described.
[0027] First, (a) shows a proportional gain controller. In the case
of the embodiment, the controller operates as a controller
performing damping control based on the vibration component signal
Sb extracted from the rotational signal, and may reduce vibration
according to gain K.
[0028] As described in the patent document 2, when rotational speed
is multiplied by a gain, and negative feedback control is performed
and thus damping control is established, the signal is controlled
such that variation in rotational speed is suppressed, and
consequently vibration may be reduced. (b) shows a case of a PID
gain controller, wherein since a phase characteristic or a gain
characteristic may be adjusted by a plurality of parameters,
appropriate vibration suppression characteristics may be obtained
for various kinds of vibration compared with a simple proportional
gain controller.
[0029] (c) shows a relay controller using a relay function. In the
case of the embodiment, for example, the controller is suitable for
suppressing disturbance having finite size of amplitude and a known
upper limit thereof, or for suppressing vibration based on a
vibration component signal extracted as a signal having an
extremely small amplitude, and the controller operates to suppress
variation like Coulomb friction. (d) shows a case of a saturation
controller using a saturation function. The controller has a
similar effect to that in a case of using the relay function, and
furthermore, has an effect of suppressing unexpected vibration such
as chattering that tends to occur in sudden change of a value as in
the case of using the relay function. The control means shown in
FIGS. 6(a) to 6(d) are typically used elements. The embodiment is
characterized in that each of the control means is combined with
the small-amplitude pass filter 8 to establish negative feedback
control with the subtractor 10, so that vibration suppression is
easily achieved.
[0030] As hereinbefore, according to the configuration of the
embodiment 1 of the invention, the steering component Ps is removed
from the rotational speed signal Sn, and a vibration component such
as torque ripple produced by a motor or disturbance from a road
surface, which has a small amplitude compared with the signal Ps,
may be accurately extracted, and vibration may be easily reduced
based on the extracted vibration component signal Sb, and therefore
feeling of a driver may be improved during steering driving.
[0031] The rotational speed detection means, which directly detects
rotational speed of a motor, has been used in the above
configuration. However, rotation angle detection means detecting a
rotation angle of a motor and rotational speed calculation means
calculating rotational speed from a detected rotation angle signal
may be used instead of the rotational speed detection means so that
a rotational speed signal is obtained.
Embodiment 2
[0032] FIG. 7 is a block diagram showing a configuration of a
control apparatus of embodiment 2 of the invention. While the
small-amplitude extraction filter 8 is used for the rotational
speed signal Sn to perform vibration suppression control in the
embodiment 1, the small-amplitude extraction filter 8 is used for
the steering torque signal t0 detected by the torque sensor 1 to
perform vibration suppression control in the embodiment 2. In FIG.
7, portions equal to or corresponding to those in FIG. 1 are shown
with the same symbols.
[0033] In the figure, steering torque in driver steering is
detected by the torque sensor 1, and the torque controller 2
calculates the assist torque current Ia based on the steering
torque signal t0 being output of the torque sensor. Next, the
steering torque signal t0 outputted by the torque sensor 1 is
filtered by the small-amplitude pass filter 8 having the
input/output characteristic as shown in FIG. 2, thereby a steering
component is removed from the steering torque signal so that the
vibration component Sb is extracted. Since a configuration and
operation of the small-amplitude pass filter 8 are the same as
those described in the embodiment 1, description of them is omitted
here.
[0034] The vibration suppression current Is is calculated by the
vibration suppression control means 9 based on the vibration
component signal Sb extracted by the small-amplitude pass filter 8,
and the current Is is added to the assist torque current Ia
outputted by the torque controller 2 by an adder 12, thereby the
target current It is obtained. The current control means 3 controls
the calculated target current It and the current Id detected by
current detection means 6 to correspond to each other, and outputs
the voltage instruction signal Sv such as PWM signal to the drive
circuit 4, so that the motor 5 is driven and thus assist torque is
generated.
[0035] Next, operation of the motor-driven power steering control
apparatus configured as above is described according to a flowchart
of FIG. 8. First, the steering torque signal .tau.0 being output of
the torque sensor 1 is read by a microcomputer, and stored into a
memory in step S201. Then, the assist torque current Ia is
calculated by the torque controller 2 based on the steering torque
signal .tau.0, and output of the torque controller is stored into
the memory in step S202. Here, the torque controller 2 may be
designed in a known manner, for example, in a manner that the
current is calculated based on a predetermined map.
[0036] Next, the vibration component signal Sb is calculated by the
small-amplitude pass filter 8 based on the steering torque signal
T0, and stored into the memory in step S203. Next, the vibration
suppression current Is is calculated by vibration suppression
control means 9 based on the vibration component signal Sb, and
stored into the memory in step S204. Then, the adder 12 adds the
assist torque current Ia outputted by the torque controller 2 and
the vibration suppression current Is outputted by the vibration
suppression control means 9 so that the target current It is
determined in step S205. Operation from the step S201 to the step
S205 is repeated for each control sample to calculate each target
current It.
[0037] Next, the vibration suppression control means 9 is
described.
[0038] When the small-amplitude pass filter 8 and the vibration
suppression control means 9 are used for the steering torque signal
T0, the means 9 operates to assist a usual disturbance suppression
effect using a gain of the torque controller 2. The steering torque
signal TO includes not only a steering component but also a
vibration component due to torque ripple, road surface disturbance
or the like, and the torque controller assists steering, and
furthermore, advantageously suppresses the vibration component by a
control gain of the controller. Generally, it is known that when an
open loop gain is made large enough compared with 1, influence of
disturbance may be reduced. In such a case, a signal advanced in
phase such as speed signal used in damping control need not be
used, and when a control gain is increased by proportional gain
control of a rotation angle or a steering torque signal, the open
loop gain is further increased, and thus influence of disturbance
may be further reduced. Any type of known control means may be used
as the vibration suppression control means 9. For example, the
configurations of FIGS. 6(a), 6(b) and 6(d) are described below as
typical examples of the means 9.
[0039] The proportional gain controller of FIG. 6(a) operates as a
controller that increases a proportional gain only for a vibration
component based on a vibration component signal extracted from
steering torque. In the PID gain controller of (b), since a phase
characteristic or a gain characteristic may be adjusted by a
plurality of parameters, appropriate vibration suppression
characteristics may be obtained for various kinds of vibration
compared with a simple proportional gain controller. For example,
even if the open loop gain may not be made large enough compared
with 1, a phase is advanced by a D gain, thereby a damping-like
effect may be obtained, and consequently vibration may be
suppressed. In the case of the saturation controller using a
saturation function of (d), the controller operates in the same way
as the proportional gain controller of (a) in a slope region, but a
value is fixed in a saturation region, which may prevent control
instructions from being increased more than necessary. The control
means shown in FIGS. 6(a), 6 (b) and 6(d) are typically used
elements, and each of the control means is combined with the
small-amplitude pass filter 8 to establish a feedback control loop,
so that vibration suppression may be easily achieved.
[0040] As hereinbefore, according to the configuration of the
embodiment 2 of the invention, the steering component is removed
from the steering torque signal T0, and a vibration component such
as torque ripple produced by a motor or disturbance from a road
surface, which has a small amplitude compared with the signal T0,
may be accurately extracted, and vibration may be reduced based on
the extracted vibration component signal, and therefore feeling of
a driver may be improved.
[0041] While the embodiment 1 or 2 shows a case where the
small-amplitude pass filter and the vibration suppression control
means are used for a rotational speed signal calculated from a
detection signal of rotational speed or a rotation angle, or used
for a steering torque signal, the filter and the means may be
further used for a rotation angle signal, an estimated rotational
speed signal estimated by an observer or the like, an estimated
steering torque signal, an steering angle or steering speed of a
steering wheel, horizontal acceleration of a car, or dynamic state
quantity of a yaw rate or the like.
BRIEF DESCRIPTION OF THE DRAWINGS
[0042] FIG. 1 It is a block diagram showing an motor-driven power
steering control apparatus according to embodiment 1 of the
invention.
[0043] FIG. 2 It is an input/output characteristic diagram showing
a small-amplitude pass filter in each of embodiments 1 and 2 of the
invention.
[0044] FIG. 3 It is a flowchart showing processing within a
microcomputer in the embodiment 1 of the invention.
[0045] FIG. 4 It is a block diagram showing a configuration example
of the small-amplitude pass filter in each of the embodiments 1 and
2 of the invention.
[0046] FIG. 5 It is temporal waveforms of input/output signals
showing an operation example of the small-amplitude pass filter in
each of the embodiments 1 and 2 of the invention.
[0047] FIG. 6 It is block diagrams showing a vibration suppression
controller in each of the embodiments 1 and 2 of the invention.
[0048] FIG. 7 It is a block diagram showing a motor-driven power
steering control apparatus according to the embodiment 2 of the
invention.
[0049] FIG. 8 It is a flowchart showing processing within a
microcomputer in the embodiment 2 of the invention.
DESCRIPTION OF THE REFERENCE NUMERALS AND SIGNS
[0050] 1 torque sensor [0051] 2 torque controller [0052] 5 motor
[0053] 6 current detection means [0054] 7 rotational speed
detection means [0055] 8 small-amplitude pass filter [0056] 9
vibration suppression control means [0057] 21 hysteresis filter
* * * * *